The disclosure relates to compressors. More particularly, the disclosure relates to electric motor-driven hermetic or semi-hermetic compressors.
One particular use of electric motor-driven compressors is liquid chillers. An exemplary liquid chiller uses a hermetic centrifugal compressor. The exemplary unit comprises a standalone combination of the compressor, the cooler unit, the chiller unit, the expansion device, and various additional components. The exemplary compressor includes a transmission intervening between the motor rotor and the impeller to drive the impeller at a faster speed than the motor.
The motor is exposed to a bypass of refrigerant flow to cool the motor. The exposure of the motor rotor to refrigerant produces losses known as windage. Windage losses increase with motor speed and with density of refrigerant exposed to the rotor.
In the United States, chillers are subject to American Refrigeration Institute (ARI) Standard 550. This standard identifies four reference conditions characterized by a percentage of the chiller's rated load (in tons of cooling) and an associated condenser water inlet/entering temperature. Operation is to achieve a chilled water outlet/leaving temperature of 44 F (6.67 C). The four conditions are: 100%, 85 F (29.44 C); 75%, 75 F (23.89 C), 50%, 65 F (18.33 C); and 25%, 65 F (18.33 C also). These conditions (or similar conditions along a curve of connecting them) may provide relevant conditions for measuring efficiency. In API testing, the water flow rate through the cooler is 2.4 gallons per minute per ton of cooling (gpm/ton) (0.043 liters per second per kilowatt (l/s/kW)) and condenser water flow rate is 3 gpm/ton (0.054 l/s/kW).